1. Field of the Invention
The present invention relates to fuel cell systems and transportation equipment including a fuel cell system, and more specifically to a fuel cell system which holds aqueous fuel solution, and to transportation equipment including the system.
2. Description of the Related Art
JP-A 2006-004680 discloses a fuel cell system in which an aqueous solution container is supplied with water from a container which holds the water.
Generally in such a fuel cell system as described above, water is supplied to the aqueous solution container in order to bring the liquid level in the aqueous solution container to a predetermined liquid level. During power generation in the fuel cell, the aqueous solution container is supplied with a mixture of aqueous fuel solution and gases such as carbon dioxide which has resulted from the power generation and a gaseous form of fuel which has resulted from evaporation in the course of circulatory supply, for example, of the aqueous fuel solution. Consequently, bubbles are produced in the aqueous fuel solution held in the aqueous solution container. In this case, the water supply to the aqueous solution container in order to bring the liquid level to the predetermined level is based on a level of bubbly liquid in the aqueous solution container which contains the bubbles.
Also, in such a fuel cell system like the one described above, it is likely that aqueous fuel solution has a high temperature and a uniform concentration if there has not been a long time passed since the last stoppage of power generation, for example, and in such a case, it will be possible to quickly shift to normal operation, i.e., the state where constant power generation is possible. In other words, it is highly probable that the state of aqueous fuel solution is ready for power generation, and that it is possible to shift to normal operation quickly.
However, in the conventional art, if bubbles are not present in the aqueous fuel solution held in the aqueous solution container, water is supplied to the aqueous solution container based on the actual level of the liquid which does not contain bubbles. In other words, a greater amount of water is supplied when bubbles are not present, than when bubbles are present. Since a large amount of water is supplied to the aqueous solution container if bubbles are not present, the state of the aqueous fuel solution is changed even if the aqueous fuel solution was ready for power generation at the time when power generating operation was stopped, and this poses a problem that a long time is necessary before the system shifts to normal operation.